Large acceptance magnetic spectrometer for the 12 GeV 2 GEp experiment (at Jefferson Lab)

1. DNP 2013 – Newport News – 26/Oct/2013 Large acceptance magnetic spectrometer for the 12 GeV2 GEp experiment(at Jefferson Lab) E. Cisbani INFN Rome – Sanità Group and Italian National Institute of Health for the SBS collaboration • Outlook • Electromagnetic form factors at high Q2 • Experimental requirements • Spectrometer details http://hallaweb.jlab.org/12GeV/SuperBigBite E. Cisbani / SBS for GEp5 @ JLab12

2. Form Factors: discovery and formalism • R.W. McAllister, R. Hofstadter Phys. Rev. 102 (1956) 851 “First measurement of the proton electromagnetic radius”: RMS E/M radius of =(0.74 ± 0.24) 10-13cm Nucleon electromagnetic current operator has two “unknown” functions (Dirac and Pauli FFs) that describe the internal structure of the nucleon (one photon exchange approx.): In terms of Sachs FFs: Sachs FFs are FT of the charge and magnetization distributions in the nucleon (in Breit frame) Elastic Cross section (Rosenbluth): E. Cisbani / SBS for GEp5 @ JLab12

3. Rosenbluth Separation: assume single photon approximation Polarization transfer from the incident electron to the scattered proton Proton GE/GM – an «unexpected» discrepancy Prior to JLab/2000, expectations were that proton GE/GM fairly constant with Q2 At JLab, new class of experiments show proton GE/GM decreasing linearly with Q2 Two Photon Exchange – favorite candidate DA3: T. Averett HA2: M. Kohl E. Cisbani / SBS for GEp5 @ JLab12

4. Proton GE/GM- Theoretical models • Many theoretical models • VMD (Iachello, Lomon, Bijker), generally good description of all FF • Relativistic CQM (Miller, Gross, ...) spin dependent quark density • Lattice QCD, start to give prediction • Dyson-Schwinger, dressed quarks, diquark correlation, ... • pQCD-based: GE/GMconst Q2 • GPD-based: direct connection to quark OAM, FF’s constraint GPD’s Most of them agree with current data but diverge at higher, unexplored, Q2 E. Cisbani / SBS for GEp5 @ JLab12

5. «Modern» Form Factor measurements at high Q2 Challenges at high Q2: Maximize (coincidence) acceptance Maximize luminosity Mazimize polarization efficiency Maximize beam polarization (... having the needed beam energy) ... keeping costs at «affordable» level E. Cisbani / SBS for GEp5 @ JLab12

6. add Hall D (and beam line) Upgrade magnets and power supplies CHL-2 Jefferson Lab - CEBAF after 2013 6 GeV CEBAF (< 2013) Max Current: 200 mA Max Energy: 0.8 - 5.7 GeV Long. Polarization: 75-85% Doubling Beam Energy 12 GeV CEBAF (>2013) Max Current: 90 mA Max Energy Hall A,B,C: 10.9 GeV Max Energy Hall D: 12 GeV Long. Polarization: 75-85% E. Cisbani / SBS for GEp5 @ JLab12

7. Proton GE/GM at large Q2 by polarization transfer (SBS) Beam: Current= 75 mA, Polarization= 85% long. Energy= 6, 8 and 11 GeV Target: H2 Liquid Length= 40 cm Luminosity = 8 · 1038 Detectors: P-arm: SBS + Polarimeter E-arm: BigCal + Coordinate GEp5 experiment in HallA GOAL: Extend the measurement of the proton form factor ratio GE/GM to the maximum Q2 that is possible with 11 GeV beam with constraints: Absolute error < 0.1 Beam time = 60 days E. Cisbani / SBS for GEp5 @ JLab12

8. New SuperBigbite Spectrometer (SBS) in Hall A • Large luminosity • “Large” acceptance • Forward angles • Reconfigurable detectors High photon up to 250 MHz/cm2 and electron 160 kHz/cm2 background • Support event rate 10x higher than with standard small acceptance spectrometer • GEM chambers to handle the high rate of the background E. Cisbani / SBS for GEp5 @ JLab12

9. Large Luminosity  Large Background Hit • Must be supported by the detectors  GEM technology • Must be handled by the trigger: • spatial and time correlation between electron and proton elastically scattered • «high» energy threshold in segmented CALO’s Good tracking resolution needed - momentum resolution: 1 % - angular resolution: 1 mrad - vertex reconstruction: 5 mm Red: p0photoproduction Black: Elastics Blue: Sum For Emiss<0.35 GeV, remaining p0 background: 10% Adequate proton polarization precession reconstruction (next slide) E. Cisbani / SBS for GEp5 @ JLab12

10. GEp5: Proton Polarimeter (PP) Number of scattered protons: Use azimuthal asymmetry of the proton scattering off matter induced by spin-orbit coupling where  refers to electron beam helicity A (a.u.) Track in Track out Pypp Pxpp Track in Track out Polarimeter only measures components of proton spin that are transverse to the proton’s momentum direction Maximize Pe N=number of scattered proton, Pe beam polarization Require: Dipole magnet to precess Pl at target to Pypp E. Cisbani / SBS for GEp5 @ JLab12

11. SBS Dipole Magnet / 48D48 from BNL • Magnet Parameters • Integral field strength 1.82 T-m2.28 T-m with pole shims • Yoke length 1.22 m • Gap: 47 cm  121.9 cm • Yoke Weight 85 tons • 6 1008 steel sectors, largest is 18.3 tons Beam • Magnetic field needed for: • Momentum measurement • Polarimetry • Sweep off low energy charged particles Yoke modifications to allow beam pipe passage at forward angle kinematics Adapted from Robin Wines / JLab E. Cisbani / SBS for GEp5 @ JLab12

12. GEM foil: 50 mm Kapton + few mm copper on both sides with 70 mm holes, 140 mm pitch Ionization Multiplication Multiplication Multiplication Readout Strong electrostatic field in GEM holes GEM Working principle Recent Technology: F. Sauli, Nucl. Instrum. Methods A386(1997)531 Support high particle flux ( MHz/cm2) Intrinsic resolution at 50 mm level Relatively unexpensive Robust / Slow aging SBS Gain vs Particle Flux E. Cisbani / SBS for GEp5 @ JLab12

13. SBS - GEM Front Tracker • Six 150x40 cm2 chambers with small dead area (~10%) • Each chamber consists of 3 50x40 cm2 lightweight 3xGEM modules with x/y strip readout (0.4 mm pitch) • Readout electronics based on high channel density APV25 ASIC driven by VME64x modules Use x/y charge correlation for false hit suppression Large SNR E. Cisbani / SBS for GEp5 @ JLab12

14. GEM Front Tracker MonteCarlo Realistic MC and digitization • Tracking efficiency 99%-85% depending on background • Track parameter resolutions at acceptable values even at largest background E. Cisbani / SBS for GEp5 @ JLab12

15. CH2 Polarimeters with GEM tracking • Two Polarimeters in series to increase statistics by ~50% • Each polarimeters consists of CH2 analyzer (50 cm) and four 50x2000 cm2 GEM chambers • Each chamber is made of five 50x50 cm2 GEM modules • Similar design of GEM front tracker, optimized for focal polarimetry (less demanding particle rate respect to main tracker) Number of scattered protons N. Liyanage et al. / UVa qpp (deg) E. Cisbani / SBS for GEp5 @ JLab12

16. PJ6: B. Quinn G. Franklin et al. / Carnegie Mellon E. Cisbani / SBS for GEp5 @ JLab12

17. High Luminosity, impact on Trigger / DAQ • Must efficienty select electron elastic scattering by angular correlation • First level (L1) from electron arm • Energy information (with cuts to reduce inelastic) • Rate (from SLAC high energy data and RCS experiments): • Hadron Arm: • Energy information (with cuts to reduce inelastic) • Rate: 1.5 MHz • Second level (L2) from two-arm coincidence: • in 30 ns gate: 9 kHz • AND geometrical correlation: 2 kHz DJ4: A. Camsonne E. Cisbani / SBS for GEp5 @ JLab12

18. Conclusions Expected results on proton GE/GM http://hallaweb.jlab.org/12GeV/SuperBigBite • SBS, is a cost effective, new magnetic spectrometer; will use the recent GEM technology to operate at high luminosity, providing “large” acceptance and high reconstruction accuracy • SBS will permit unprecedented measurements of the proton and neutron Form Factors at high Q2 as well on SIDIS physics Likely from 2016 NC9: A. Puckett E. Cisbani / SBS for GEp5 @ JLab12